The present invention relates to a system for transporting, loading and unloading slabs and tiles, and more particularly, slabs or tiles of any of stone, granite, marble, mineral, glass, porcelain, plaster, polymer, wood, and precast cement or any like material of high density, low value which is normally transported in slab or sheet form.
In the past, transported slabs were unloaded and stored on open A-frames with the slabs held together by tension wrap. Removing or unloading slabs from A-frames is problematic as a vacuum is created when slabs are pulled apart, and pulling too quickly can cause other slabs to follow in succession. If control is lost, multiple slabs can fall over possibly breaking the slabs and/or endangering the workers. Unloading a conventional A-frame containing 20 industry standard granite slabs typically requires two hours and three men. Tension wraps are unsatisfactory because they weaken slab edge areas which sometimes can break away. Before shipping containers were developed, slabs, such as granite, had to be packaged very carefully on A-frames with heavy dunnage because slabs must be shipped on edge and granite is relatively heavy and very brittle, breaking easily in transportation. Also, A-frames consume warehouse resources inefficiently and loaded A-frames cannot be stacked top to bottom.
In the mid 50's, a trucker, Malcolm McLean, invented shipping containers. He revolutionized the shipping industry and was responsible for the original Sea-Land container ships which are now used globally. Using containers for transporting granite was an improvement on the earlier break bulk methodology and involves packaging up to 10 slabs ¾″ thick in wooden packages called bundles with generally seven bundles loaded into a container. Traditional shipping containers are standardized at 20×8×8 feet and were designed for low density, high value cargo, but are not suitable for high density, low value cargo such as stone, which has a density of approximately 175-200 pounds per cubic feet. Twenty tons of stone are equivalent to 200-225 cubic feet of space which means that over 1,000 cubic feet or 80% of the container capacity goes unfilled. Also, stone or glass sheets are fragile and must be shipped upright, and because of the volume of wasted space, must be blocked and braced to prevent toppling and damage during transit. In heavy seas, nails will pull out and the bundles will fall apart. This loosening effect is dangerous to the laborers involved in stripping the container and when this happens, an entire container of stone worth perhaps $100,000 can be lost.
There is another drawback in that the wood used for packaging and dunnage must be fumigated for U.S. agricultural reasons and because the wood has, by definition, been chemically treated, it must then be disposed of professionally in HazMat sites. Finally, because of the volume of wood used for blocking and bracing, clearing a container takes extensive time, generally in excess of half a day employing four people.
There is also a safety drawback. On arrival at the destination, a laborer is sent into the container with a chainsaw to cut away the dunnage. If this is done carelessly, a bundle can topple pinning the laborer between the wall of the container and perhaps 10,000 pounds of stone. In the last 10 years or so, there have been no fewer than several hundred accidents, many of them fatal.